Protein kinases are a family of enzymes that catalyze phosphorylation of proteins, in particular the hydroxyl group of specific tyrosine, serine, or threonine residues in proteins. Protein kinases are pivotal in the regulation of a wide variety of cellular processes, including metabolism, cell proliferation, cell differentiation, and cell survival. Uncontrolled proliferation is a hallmark of cancer cells, and can be manifested by a deregulation of the cell division cycle in one of two ways making stimulatory genes hyperactive or inhibitory genes inactive. Protein kinase inhibitors, regulators or modulators alter the function of kinases such as Akt kinases, Checkpoint (CHK) kinases (e.g., CHK-1, CHK-2 etc.), Aurora kinases, Pim kinases (e.g., Pim-1, Pim-2, Pim-3 etc.), tyrosine kinases and the like.
Checkpoint kinases prevent cell cycle progression at inappropriate times, such as in response to DNA damage, and maintain the metabolic balance of cells while the cell is arrested, and in some instances can induce apoptosis (programmed cell death) when the requirements of the checkpoint have not been met. Checkpoint control can occur in the G1 phase (prior to DNA synthesis) and in G2, prior to entry into mitosis.
One series of checkpoints monitors the integrity of the genome and, upon sensing DNA damage, these “DNA damage checkpoints” block cell cycle progression in G1 & G2 phases, and slow progression through S phase. This action enables DNA repair processes to complete their tasks before replication of the genome and subsequent separation of this genetic material into new daughter cells takes place. Inactivation of CHK1 has been shown to transduce signals from the DNA-damage sensory complex to inhibit activation of the cyclin B/Cdc2 kinase, which promotes mitotic entry, and abrogate G2 arrest induced by DNA damage inflicted by either anticancer agents or endogenous DNA damage, as well as result in preferential killing of the resulting checkpoint defective cells. See, e.g., Peng et al., Science, 277, 1501-1505 (1997); Sanchez et al., Science, 277, 1497-1501 (1997), Nurse, Cell, 91, 865-867 (1997); Weinert, Science, 277, 1450-1451 (1997); Walworth et al., Nature, 363, 368-371 (1993); and Al-Khodairy et al., Molec. Biol. Cell., 5, 147-160 (1994).
Selective manipulation of checkpoint control in cancer cells could afford broad utilization in cancer chemotherapeutic and radiotherapy regimens and may, in addition, offer a common hallmark of human cancer “genomic instability” to be exploited as the selective basis for the destruction of cancer cells. A number of factors place CHK1 as a pivotal target in DNA-damage checkpoint control. The elucidation of inhibitors of this and functionally related kinases such as CDS1/CHK2, a kinase recently discovered to cooperate with CHK1 in regulating S phase progression (see Zeng et al., Nature, 395, 507-510 (1998); Matsuoka, Science, 282, 1893-1897 (1998)), could provide valuable new therapeutic entities for the treatment of cancer.
Another group of kinases are the tyrosine kinases. Tyrosine kinases can be of the receptor type (having extracellular, transmembrane and intracellular domains) or the non-receptor type (being wholly intracellular). Receptor-type tyrosine kinases are comprised of a large number of transmembrane receptors with diverse biological activity. In fact, about 20 different subfamilies of receptor-type tyrosine kinases have been identified. One tyrosine kinase subfamily, designated the HER subfamily, is comprised of EGFR (HER1), HER2, HER3 and HER4. Ligands of this subfamily of receptors identified so far include epithelial growth factor, TGF-alpha, amphiregulin, HB-EGF, betacellulin and heregulin. Another subfamily of these receptor-type tyrosine kinases is the insulin subfamily, which includes INS-R, IGF-IR, IR, and IR-R. The PDGF subfamily includes the PDGF-alpha and beta receptors, CSFIR, c-kit and FLK-II. The FLK family is comprised of the kinase insert domain receptor (KDR), fetal liver kinase-1(FLK-1), fetal liver kinase-4 (FLK-4) and the fms-like tyrosine kinase-(flt-1). For detailed discussion of the receptor-type tyrosine kinases, see Plowman et al., DN&P 7(6): 334-339, 1994.
At least one of the non-receptor protein tyrosine kinases, namely. LCK, is believed to mediate the transduction in T-cells of a signal from the interaction of a cell-surface protein (Cd4) with a cross-linked anti-Cd4 antibody. Amore detailed discussion of non-receptor tyrosine kinases is provided in Bolen. Oncogene, 8, 2025-2031 (1993). The non-receptor type of tyrosine kinases is also comprised of numerous subfamilies, including Svc, Frk, Btk, Csk, Abl, Zap70, Fes/Fps, Fak, Jak, Ack, and LIMK. Each of these subfamilies is further sub-divided into varying receptors. For example, the Src subfamily is one of the largest and includes Src, Yes, Fyn, Lyn, Lck, Blk, Hck, Fgr, and Yrk. The Src subfamily of enzymes has been linked to oncogenesis. For a more detailed discussion of the non-receptor type of tyrosine kinases, see Bolen, Oncogene, 8:2025-2031 (1993).
In addition to its role in cell-cycle control, protein kinases also playa crucial role in angiogenesis, which is the mechanism by which new capillaries are formed from existing vessels. When required, the vascular system has the potential to generate new capillary networks in order to maintain the proper functioning of tissues and organs. In the adult, however, angiogenesis is fairly limited, occurring only in the process of wound healing and neovascularization of the endometrium during menstruation. On the other hand, unwanted angiogenesis is a hallmark of several diseases, such as retinopathies, psoriasis, rheumatoid arthritis, age-related macular degeneration, and cancer (solid tumors). Protein kinases which have been shown to be involved in the angiogenic process include three members of the growth factor receptor tyrosine kinase family; VEGF-R2 (vascular endothelial growth factor receptor 2, also known as KDR (kinase insert domain receptor) and as FLK 1); FGF-R (fibroblast growth factor receptor); and TEK (also known as Tie-2).
VEGF-R2, which is expressed only on endothelial cells, binds the potent angiogenic growth factor VEGF and mediates the subsequent signal transduction through activation of its intracellular kinase activity. Thus, it is expected that direct inhibition of the kinase activity of VEGF-R2 will result in the reduction of angiogenesis even in the presence of exogenous VEGF (see Strawn et al, Cancer Research, 56, 3540-3545 (1996)), as has been shown with mutants of VEGF-R2 which fail to mediate signal transduction. Millauer et al, Cancer Research, 56, 1615-1620 (1996). Furthermore, VEGF-R2 appears to have no function in the adult beyond that of mediating the angiogenic activity of VEGF. Therefore, a selective inhibitor of the kinase activity of VEGF-R2 would be expected to exhibit little toxicity.
Similarly. FGFR binds the angiogenic growth factors aFGF and bFGF and mediates subsequent intracellular signal transduction. Recently, it has been suggested that growth factors such as bFGF may play a critical role in inducing angiogenesis in solid tumors that have reached a certain size. Yoshiji et al., Cancer Research, 57, 3924-3928 (1997). Unlike VEGF-R2, however, FGF-R is expressed in a number of different cell types throughout the body and may or may not play important roles in other normal physiological processes in the adult. Nonetheless, systemic administration of a small molecule inhibitor of the kinase activity of FGF-R has been reported to block bFGF-induced angiogenesis in mice without apparent toxicity. Mohammad et al., EMBO Journal, 17, 5996-5904 (1998).
TEK (also known as Tie-2) is another receptor tyrosine kinase expressed only on endothelial cells which has been shown to play a role in angiogenesis. The binding of the factor angiopoietin-1 results in autophosphorylation of the kinase domain of TEK and results in a signal transduction process which appears to mediate the interaction of endothelial cells with peri-endothelial support cells, thereby facilitating the maturation of newly formed blood vessels. The factor angiopoietin-2, on the other hand, appears to antagonize the action of angiopoietin-1 on TEK and disrupts angiogenesis. Maisonpierre et al., Science, 277, 55-60 (1997).
Pim-1 is a small serine/threonine kinase. Elevated expression levels of Pim-1 have been detected in lymphoid and myeloid malignancies, and recently Pim-1 was identified as a prognostic marker in prostate cancer. K. Peltola, “Signaling in Cancer: Pim-1 Kinase and its Partners”, Annales Universitatis Turkuensis, Sarja—Ser. D Osa-Tom. 616, (Aug. 30, 2005), http://kirjasto.utu.fi/julkaisupalvelut/annaalit/2004/D616.html. Pim-1 acts as a cell survival factor and may prevent apoptosis in malignant cells. K. Petersen Shay et al., Molecular Cancer Research 3:170-181 (2005).
References of interest in regard to the present invention are: A. Bullock et al., J. Med. Chem., 48 (2005), 7604-7614; A. Bullock et al., J. Biol. Chem., 280 No. 50 (2005), 41675-41682; D. Williamson et al, J. Bioorg. Med. Chem. Lett., 15 (2005), 863-867; and patents and patent publications: US2006/0135526; WO2003/095455; WO2006/044958; US2006/0135514; US2004/081013; US2006/0053568; WO2001/23388; WO2004/087707; WO2003/093297; WO2002/070494; U.S. Pat. No. 6,313,124; FR2874821; WO2005/070431; US2005/0222171; US2005/0107386; and JP2006/160628.
Pyrazolopyrimidines are known. For example, WO92/18504, WO02/50079, WO95/35298, WO02/40485, EP94304104.6, EP0628559 (equivalent to U.S. Pat. Nos. 5,602,136, 5,602,137 and 5,571,813), U.S. Pat. No. 6,383,790, Chem. Pharm. Bull., (1999) 47 928, J. Med. Chem., (1977) 20, 296, J. Med. Chem., (1976) 19 517 and Chem. Pharm. Bull., (1962) 10 620 disclose various pyrazolopyrimidines. Other publications of interest include: U.S. Pat. Nos. 5,688,949 and 6,313,124, WO 98/54093, WO 03/101993, WO 03/091256, WO 04/089416 and DE 10223917.
The following patents and patent applications disclose several types of pyrazolopyrimidines and are incorporated herein in their entirety by reference: (i) Ser. No. 11/245,401 filed Oct. 6, 2005 and published as US 2006/0128725 on Jun. 15, 2006), (ii) Ser. No. 10/654,546, filed Feb. 11, 2004, and published as US 2004/0209878 on Oct. 21, 2004, (iii) Ser. No. 11/244,772, filed Oct. 6, 2005, and published as US 2006/0041131 on Feb. 23, 2006, (iv) Ser. No. 11/244,776, filed Oct. 6, 2005, and published as US 2006/0040958 on Feb. 23, 2006, (v) Ser. No. 10/654,163 filed Sep. 3, 2003, published as US 2004/0102452 on May 27, 2004, and granted as U.S. Pat. No. 7,084,271 on Aug. 1, 2006, and (vi) Ser. No. 10/653,868 filed Sep. 3, 2003, published as US 2004/0116442 on Jun. 17, 2004, and granted as U.S. Pat. No. 7,074,924 on Jul. 11, 2006. Additionally, (vii) U.S. application Ser. Nos. 11/542,920, (vii) 11/542,921, (ix) 11/542,833, and (x) 11/543,182, all four commonly owned and being filed of even date herewith, are also incorporated herein in their entirety by reference. The disclosures in the foregoing references (i) through (x) cited above in this paragraph should be considered part of the present invention.
There is a need for methods to inhibit protein kinases to treat or prevent disease states associated with abnormal cell proliferation. Moreover, it is desirable for such methods to use kinase inhibitors that possess both high affinity for the target kinase as well as high selectivity versus other protein kinases. Useful small-molecule compounds that may be readily synthesized and are potent inhibitors of cell proliferation are those, for example, that are inhibitors of one or more protein kinases, such as Akt (e.g., Akt-1, Akt-2, Akt-3), CHK1, CHK2, VEGF (VEGF-R2), Aurora (e.g., Aurora-1, Aurora-2, Aurora-3 etc), Pim-1 and both receptor and non-receptor tyrosine kinases.